This invention relates generally to a radial tire for a passenger car, and more particularly to a radial tire for a passenger car having an improved structure for the portion of the tire ranging from bead portions to its side wall portions in order to improve driving stability and durability without reducing driving comfortableness.
Generally, radial tires consist of a pair of right and left bead portions, a pair of right and left side wall portions continuing the bead portions, respectively, and a tread portion interposed between the side wall portions. Furthermore, a carcass layer having a cord angle in the range of 70.degree. to 90.degree. in a tire circumferential direction is fitted between the bead portions, and a plurality of belt layers which have cord angles of 10.degree. to 35.degree. in the tire circumferential direction and in which the cords of one of the belt layers cross those of the other belt layers is disposed on the carcass layer at the tread portion.
In the radial tire of the type described above, since the reinforcing cords of the carcass layer are arranged substantially at right angles to the tire circumferential direction, deformation of the side wall portions is easy to develop during driving. Therefore, although good driving comfortableness can be obtained in a vertical direction, the delay of maneuvering response and unstability are likely to occur in a longitudinal direction as well as in a transverse direction due to excessive deformation.
Means for improving the problem resulting from the excessive deformation described above while maintaining good driving comfortableness is disclosed, for example, in Japanese Patent Application Kokai Publication No. 57-18503 and Japanese Patent Publication No. 56-47004.
In Japanese Patent Application Kokai Publication No. 57-18503, a reinforcing layer is disposed in close contact with the outer or inner side of a bead filler in such a manner as to extend in the range of 50 to 75% of the sectional height of the tire.
If the reinforcing layer is disposed outside the bead filler, it undergoes compressive deformation in the proximity of a rim flange, while it undergoes compressive deformation at the side wall portions when it is disposed inside the bead filler. Therefore, durability of the tire, particularly its high speed durability and load durability, cannot be improved. Moreover, since the upper half of the reinforcing layer passes through a neutral axis, rigidity cannot be increased and driving stability cannot be improved.
Therefore, this prior art reference attempts to obtain the reinforcing effect by disposing the reinforcing layer in such a manner as to extend beyond 50% of the tire sectional height. As a result, a flex zone (bending zone) becomes extremely narrow and driving comfortableness drops.
On the other hand, Japanese Patent Publication No. 56-47004 disposes the reinforcing layer along the neutral axis.
Therefore, the reinforcing layer receives neither compressive stress nor tensile stress so that the rigidity improving effect by the disposition of the reinforcing layer is small and driving stability cannot be improved.
As described above, the conventional means are not entirely satisfactory in obtaining the intended effects.